Considering the scale of the operation, the roll-out of the New Xbox Experience went pretty damn well. Didn't, however, go perfectly. There were a few glitches here and there. Netflix took a while to get going (though that problem was likely to have been on Netflix's end of things), but more pressingly, the XBL Marketplace has been patchy ever since launch. For a lot of people, either you can access it and it's really, really slow, or you can't access it at all. If it's any comfort, Microsoft know it's broken, Larry Hryb writing on his blog:

As you can imagine, it's been an incredible day so far for the New Xbox Experience. It's great to see so much enthusiasm…it sounds like you are having fun exploring NXE. With an update of this magnitude, reaching more than 14 million people around the globe, we are aware some of you may be experiencing a few hiccups along the way. The LIVE team is closely monitoring the LIVE service and Xbox.com and are aware of a few issues including what's happening with Marketplace. The team is actively working on the issues, so thanks for bearing with us.

Me, I can access the marketplace, but it's slow going. Hopefully everything settles down in a day or so, when there's not millions of people using it at once. NXE Launch Day Update [Microsoft]